Heat Exchange Apparatus For The Utilisation Of The Heat Content Of Exhaust Gases

Abstract

Heat transfer apparatus for the utilization of the heat content of exhaust gases includes two heat-exchangers linked by a closed circuit in which an intermediate medium circulates. There is a special device for restricting or stopping the flow of the intermediate medium which receives heat in one of the heat-exchangers from the hot exhaust gases and transfers it to the heat-receiving medium in the other heat-exchanger.

Description

The invention concerns heat transfer apparatus for the utilization of the heat content of exhaust gases.

In heating technology there often occurs the task of utilization of hot gases in inexpensive and well controllable apparatus for the purpose of heating or evaporating some heat-receiving medium (usually water).

Special problems arise when the production of the hot gases is not in step with the criterion for the intake of heat of the heat-receiving medium. This is the case where e.g. the hot gases are exhaust gases and the heat-receiving medium is water to be used for heating; it often occurs that at a given instant there is no actual need for heating, yet exhaust gases are still being formed. In such cases the known regulating methods either cannot be used or require very expensive equipment.

From the point of view of apparatus regulation, there is known a solution wherein the heat intake of the heat-receiving medium is regulated by varying the quantity and/or temperature of the exhaust gases; further, another solution is known, wherein the quantity of steam produced is regulated by varying the rate of the surface area that is being exposed or "flooded" (in this case, the heat-receiving medium is evaporated in a large volume apparatus by being directly heated by the hot gases).

Regulation by varying the quantity of gases can be effected, in the above-mentioned case, by a drawing-off method, but this can only be done in principle, for the required sealing device always leak and the leakage of hot gases results in either an impermissible increase in pressure on the "secondary" side, or in the impermissible heating or evaporation of the water flowing through the apparatus. Moreover, sealing devices suitable for drawing off gases are expensive.

In the case of regulation by varying the area of exposure the heat-exchanging surfaces very rapidly become covered by scales, since all heat-receiving medium coming into contact with the heating surface is evaporated, therefore there is no rinsing, and furthermore the surfaces become hot by being in contact with hot smoke gases. Because of the rapidly deteriorating heat transfer efficiency, extremely large surfaces must be provided and they must often be cleaned, and also associated conduits are often damaged.

There is a further known solution wherein the hot gases serve to evaporate some intermediate medium, and the heat-receiving medium to be heated or evaporated takes up its heat in a condenser for the intermediate medium. In this case the hitherto known method of control consists of the heat-receiving medium being allowed to take up all the heat it can from the hot gases, but some third, auxiliary cooling medium is provided promptly to draw off excess heat at a further heat-exchange surface from the heat-receiving medium.

This last solution was conceived to obviate the drawbacks of the long known, practically "classic," solutions of the problem described above, and gives superior results. However, a grave disadvantage of even this solution is that it requires a third cooling medium to operate it, also it is complicated and expensive, requiring a three-way heat-exchange apparatus for its achievement.

An intermediate medium is also used for heat transfer in the so-called Schmidt-Hardtmann boiler, well-known in boiler construction. However, as this boiler has its own combustion apparatus, and naturally regulation is here effected by controlling the combustion apparatus.

It is to be noted that with this type of boiler it is an essential condition, for basic security reasons, that there should be no flow-restricting means in the circulation path of the intermediate medium.

This invention seeks the elimination of the above disadvantages and the provision of a heat transfer apparatus for the utilization of the heat-content in exhaust gases, wherein steam production is controllable by very simple means and is terminable even without the stoppage of flow of exhaust gases. The invention is based on the recognition that the above aim may be achieved if the utilization of the heat of the exhaust gases is effected by an intermediate medium, and a specially formed fluid flow restricting or terminating device is inserted into the circulation path of the intermediate medium.

According therefore to the present invention, there is provided heat transfer apparatus for the utilization of the heat content of exhaust gases, including a first heat-exchanger adapted to have an intermediate medium supplied thereto and placed in the path of the exhaust gases for the evaporation of the intermediate medium, said first heat-exchanger being connected in a closed fluid flow circuit to a second heat-exchanger which is adapted to condense the vapour of the intermediate medium in heat exchange with a heat-receiving medium and which is provided with a deaerating means, there being ducting between the two heat exchanges in which is disposed a device for the restriction or elimination of the flow of liquid between said heat-exchangers.

In an advantageous preferred embodiment of this invention the air exhausting or deaerating means is a gas container provided with natural or artificial cooling means which is connected to the condenser heat exchanger partly directly and partly via a flow seal.

The invention is described in detail, by way of examples, with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic circuit diagram of a preferred embodiment of the apparatus according to this invention.

FIG. 2 is a schematic diagram of a modified embodiment of the apparatus according to this invention,

FIGS. 3 and 4 are further schematic illustrations of preferred embodiments of the apparatus according to this invention, and

FIG. 5 is a still further schematic illustration of preferred embodiments for assembling the apparatus according to this invention.

Referring to the drawings, the FIG. 1 apparatus incorporates an intermediate medium in a closed circuit in which are arranged an evaporating heat exchanger 11 and a condensing heat exchanger 9. An air exhausting or deaerating means 5 is connected to the condensing heat exchanger 9, while between the condensing heat exchanger 9 and the evaporating heat exchanger 11 is inserted a device 1 for restricting or stopping the fluid flow. Examples of the construction of the device 1 are shown in FIGS. 3 and 4, and are explained with reference thereto.

In the case of the FIG. 1 embodiment, in operation exhaust gases 12 evaporate a completely pure intermediate medium in the heat exchanger 11, and the vapour 2 of the intermediate medium is passed to the condensing heat exchanger 9 by way of ducting 22, whereby to heat or evaporate the heat-receiving medium 3 which flows through the heat exchanger 9.

Having regard to the fact that the intermediate medium is completely pure, there is no need to fear scaling-up due to imperfect exposure, therefore problems connected with regulating the degree of exposure (or flooding). When there is no further need for the warming up or evaporating the intermediate medium 3, the flow of the intermediate medium is stopped by means of device 1, whereupon the supply of evaporating and heat exchanging liquid is interrupted and heat transfer through the intermediate medium ceases.

For the correct operation of the apparatus, the condensing heat exchanger 9 of the intermediate medium must be deaerated. Deaeration may be achieved by a per se known method: on starting up of the apparatus, when the pressure of the intermediate medium still esceeds the atmospheric pressure, the deaerating means 5 is actuated. The disadvantage of this method is that manual actuation is required for the deaerating means 5 which is preferably in the form of a simple tap; also with the air a portion of the vapor of the intermediate medium is also removed from the system which thus requires frequent topping-up.

Deaeration may advantageously be obtained by the embodiment shown in FIG. 2. Here the deaerating means 5 is constituted by a gas container 4 having a natural or artificial cooler 6; the upper part of the container being connected by way of a duct 7 to the deaerating outlet of heat exchanger 9, while its lower part is connected to the condensing heat exchanger 9 by way of a fluid lock 8. While the system is inoperative, pressures are small and non-condensing gases can be found everywhere. However, as soon as steam production commences, i.e. flow of the heat-receiving medium 3 through the heat exchanger 9 begins, the pressure in the circuit of the intermediate medium rises and condensation of the intermediate medium starts up also. The condensation of the intermediate medium terminates, however, in the cooled gas container 4. A steam-vapour mixture arrives in the gas container 4, but only liquid leaves it, and for this reason all non-condensing gases to be found in the system collect here; that is to say, the condensing heat exchanger 9 is deaerated.

The liquid supply to the heat exchange surface heated by hot smoke gases can be regulated by known means, e.g. by valves. There is the attendant disadvantage, however, that in time all valves develop leaks. Thus the heating surface will receive liquid even when the valves are closed. This has the result that, when cooling is absent, the pressure of the intermediate medium soon becomes impermessibly great. The valves, cocks, etc. therefore require constant maintenance and care, which in itself is a disadvantage, and further this solution has the harmful consequence that each repair involves loss of intermediate medium as well, thus necessitating topping-up.

All these disadvantages can be eliminated if the following procedure is employed.

One mode of construction of the device 1 for restricting or stopping the fluid flow is shown in FIG. 3. Here the device 1 is in the form of an inverted U-shaped tube 14, 17 whose upper part is constituted by a chamber incorporating a baffle 21 and of the U-shaped tube 14, 17 is such that normally the flow of intermediate medium cannot penetrate therethrough. In limb 14 of the U-shaped tube 14, 17 a heating means 16 is disposed.

When it is desired to start evaporating the medium 3 the heater 16 is switched on, which results in the formation of steam bubbles in the limb 14. The liquid level will then rise and will tumble over the baffle 21 to pass to the evaporating heat exchanger 11, wherein it evaporates and thus the circular flow of the intermediate medium begins and is maintained while the heater 16 remains in operation. The duct 18 serves to pass steam generated by the heater 16 to the condensing heat exchanger 9.

Another example of construction of the device 1 embodied in the apparatus according to the invention can be seen in FIG. 4. Here the inverted U-shaped tube 14, 17 has a vessel 23 connected to its uprising limb 14. The vessel 23 is provided with a heater 25 and/or a cooler 26, and is connected to the condensing heat exchanger 9 by way of a restrictor 24. In the apparatus according to this embodiment the device 1 operates as follows. When the vessel 23 is heated by heater 25, the steam formed displaces the liquid, consequently the quantity of liquid in limb 14 of the U-shaped tube increases, reaches the top of the tube, and flows over it, i.e. the flow of the intermediate medium into the evaporating heat exchanger 11 commences.

When the vessel 23 is cooled, which may be by natural cooling also, then the steam condenses and the vessel 23 fills with liquid. Thus the liquid level falls in the limb 14 of the U-shaped tube and flow of the intermediate medium into the evaporating heat exchanger ceases.

A further possible solution for the apparatus may be obtained by allowing a part of the steam generated in vessel 23 by heater 25 continuously to pass out of the system via restrictor 24. However, when the heater 25 is on, a part of the steam generated cannot pass out through the restrictor 24 and no fresh steam is generated, consequently the vessel 23 will once more fill up with liquid.

The restrictor 24 and the cooler 26 may be employed simultaneously. The apparatus according to the invention can also be realised by employing cooler 26 and restrictor 24 only. In this case the cooler, as it were, sucks the liquid into the vessel 23 and cessation of cooling results in the vessel 23 filling up with steam via restrictor 24, and the liquid level will rise in the tube limb 14.

The apparatus according to this invention provides, beyond the above-described favourable properties, special possibilities for connecting up its integers which in turn become the source of further advantages. In the case of apparatus where considerable energy is required for the heating of the liquid flow restricting means, the following combined apparatus may be constructed (see FIG. 5).

The fundamental portion of the apparatus is the apparatus according to this invention shown in FIG. 3 or FIG. 4. To this is connected a considerably smaller apparatus, also according to this invention, for utilizing the heat content of exhaust gases in such a manner that the heater 25 of the liquid flow restricting device of the fundamental, large output apparatus and the condenser of the small output apparatus together constitute a common heat transfer device: on the side of the surface of the heat transfer device the steam of the intermediate medium of the small output apparatus condenses, on the other side takes place the heating required for the operation of the liquid flow restricting device of the large output apparatus.

Regulation of the combined plant is similar to that of the simple apparatus: when the heating of the liquid flow restricting device of the small output apparatus is switched on, then this will furnish heat for the liquid flow restricting device of the large output apparatus, and the large output apparatus commences its operation. Stopping operation is effected by switching off the heating in the small output apparatus By way of example, a combination is shown in FIG. 5 where both the small output and large output apparatus is constructed in accordance with FIG. 4. However, there is no obstacle to either apparatus being constructed differently, e.g. according to the example of embodiment shown in FIG. 3.

The advantage of the apparatus is self-evident: the regulation and stopping described in the introduction can take place under the same favourable conditions, but with the expenditure of considerably smaller auxiliary energy, which is advantageous for large outputs.

Claims

We claim:

1. Heat transfer apparatus for the utilization of the heat content of exhaust gases, including a first heat-exchanger placed in the path of the exhaust gases, a second heat-exchanger, means for supplying a heat-receiving medium to the second heat-exchanger, a closed flow circuit connecting said heat-exchangers, a heat-exchange medium circulating, in operation, in said circuit so as to be heated in the first heat-exchanger and cooled in the second heat-exchanger, deaerating means for the second heat-exchanger, a device for restricting the flow of liquid heat-exchange medium between said heat-exchangers, said device being in the form of an inverted U-tube having an uprising limb and a downcoming limb, said uprising limb being connected at its top to the second heat-exchanger, and a heater for said uprising limb.

2. Apparatus as claimed in claim 1 wherein the deaerating means includes a coolable container, cooling means for said container, and flow lock, the said container being connected to the second heat-exchanger both directly and by way of said flow lock.

3. Apparatus as claimed in claim 1, said heater being disposed at the lower end of said uprising limb whereby said uprising limb serves as a vapor lift.